FIBERTEK, INC.

Design, Qualification, and On Orbit Performance of the CALIPSO Aerosol Lidar Transmitter

Floyd Hovis, Greg Witt, Ed Sullivan, and Khoa LeFibertek IncFibertek, Inc

Carl Weimer and Jeff Applegate, Ball Aerospace & Technologies Corp.

William Luck, Ron Verhapen and Michael CisewskiNASA Langley Research Center

https://ntrs.nasa.gov/search.jsp?R=20080013393 2020-06-26T02:52:24+00:00Z

FIBERTEK, INC.

Presentation Overview

Requirements

Design overview

Approach to qualificationApproach to qualification

On-orbit laser transmitter performance

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Performance Requirements

1064 nm energy 100-125 mJ

Laser performance requirements are not particularly stressing from a laser design viewpoint

1064 nm energy 100-125 mJ

532 nm energy 100-125 mJ

Pulse width 15 ns < Δt < 50 ns

Repetition rate 20 Hz

Beam quality < 10 mm-mrad, both λ

1064 nm line width < 150 pm

532 nm line width < 35 pm

532 nm polarization > 100:1 linear

Beam co-linearity < 10 % of output divergence

Beam jitter < 10 % of output divergence

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Beam jitter < 10 % of output divergence

FIBERTEK, INC. Performance Requirements

Lifetime of 2 billion shots

Pure conduction cooling

System level requirements are more challenging

Pure conduction cooling

Fully redundant lasers and electronics

Modest thermal requirements– Operate within specification in a +/- 5°C band around optimum (~20°C)p p p ( )– Operate without damage from -5°C to 30°C– No impact from non-operational -30°C to +60°C thermal cycling

Power requirements are somewhat challenging– No more than 20 W required in standbyNo more than 20 W required in standby– No more than 102 W required operationally

Severe vibrational requirements (>10.5 grms)

Dual wavelength energy monitors with +/-2% precision over full orbitg gy p– Based on integrating sphere technology

100 µrad +/- 10 µrad final divergence required matched shimming of Beam Expander Optics to each laser

Electro Magnetic Interference specification

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Electro-Magnetic Interference specification

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Optical Design Overview

• Crossed porro prism resonator for alignment insensitivity • Dual wavelength energy monitor with < +/-1% precision• Second harmonic generation with KTP• Diode pumped Nd:YAG slab gain medium• Conductively cooled

Dual wavelength energy monitor

SHG

532/1064 nmoutput

Porro prisms

R t Diode –pumped Nd:YAG slab

Q-switch

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Crossed porro prism resonator

Retro-reflector

Diode pumped Nd:YAG slab

FIBERTEK, INC. Laser System Overview

LEU

Fully redundant lasers and electronics

Sealed laser canisters– Operation in air is is better

characterized from extensive lifetime testing

– Reduced sensitivity to trace contamination

LOM #1

contamination

High efficiency electronics– Dynamic diode voltage control

#1

LOM #2

6Laser Electronics Unit

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Pre-Launch Laser Stability0 015

Energy monitor precision over full orbit ≤ 2%

Shot-to-shot energy jitter is ≤ 1.1%

532 nm wavelength varies ~ 20 pm over a 10°C change

0.005

0.010

0.015

min

al (5

32.2

13nm

) LOM#1

LOM #2

Value is consistent with the temperature shift of the Nd:YAG emission profile

Laser output energy unchanged since delivery in 2002

-0.010

-0.005

0.000

ΔλR

elat

ive

to N

om

532 nm wavelength vs. laser head temperature

> 99.5% of the of the pulses had pointing jitter that was <10% of the full beam divergence

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Pedestal Temperature (C)

-0.01515 16 17 18 19 20 21 22 23 24 25

3

4

1064 nm

532 nm

or R

eadi

ng

1

2

113.4

116.9

Max

± 0.031

± 0.031

s

4.12

3.84

Max

Convert to energy (mJ)Raw reading (Volts)

3.96

3.64

Min

111.4

112.8

Average

109.6

109.2

Min

± 0.74.0341064 nm:

± 1.13.735532 nm:

sAverage

Ene

rgy

Mon

ito

7Shot-to-shot energies

00 100 200 300 400 500 600 700 800 900 1000

Time (seconds)

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Laser Efficiency

RRL measurements with the RRL show that higher efficiencies are achieved with higher pulse energies

Two key efficiency drivers: 1) electrical power conversion efficiency & 2) spectral overlap of diodes with Nd:YAG absorption bands

Electrical power conversion efficiency of 83%

Spectral overlap somewhat off peak due to requirement to match peak 532 nm etalon transmission

LOM 1 wall plug efficiency was 4.2% (4.4 W output for 104 W total electrical input)

LOM 2 wall plug efficiency was 4.4% (4.4 W output for 100 W total electrical input)

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6RRL Efficiency Measurements

cien

cy (%

)

3

4

Effi

1

2

8

0 50 100 150 200 2500

Output Pulse Energy (mJ)

FIBERTEK, INC. Integrated Laser Transmitter

Radiator

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Beam Expanding Optics (BEOs)

FIBERTEK, INC. Laser Environmental Qualification

A systematic approach to laser qualification, beginning at the optical subassembly level and proceeding incrementally to the full module level, resulted in the successful qualification of both Laser Optic Modules as well as the Laser Electronics Unit

Optical component M d l ib ti LOM & LEU

Nd:YAG slabC b

Optical component and subassembly

testingDiode-pumped laser head burn in

Module vibration and seal testing

Burn-in

Th l/ l

LOM & LEU qualification testing

Corner cubeSteering prism TelescopePorro prismQ-switch

Canister seal testing

C i t / ti l

Thermal/vac seal test

Vibration testingQ-switchSecond harmonic

generatorDiode arrays

Canister/optical bench vibration testing

Operational vacuum testing

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FIBERTEK, INC. Laser Optics Module Qualification

Qualification Flow Plan

HeliumBench/Canister Thermal Vacuum Thermal Cycling BaselineHelium

Four –30°C to +60°C cycles 100 hour operational burn-in

HeliumHelium

Fill

Bench/Canister Integration

Thermal Vacuum Seal Test

Thermal Cycling and Burn-In

Baseline Performance Test

Vibration Test Thermal VacuumFunctional Test

Purge

Four –30°C to +60°C cycles

PurgeFill

Vibration Test Thermal Vacuum Seal Test

Functional Test

Operational Acceptance Test Flight LaserOperational Vacuum Test

Acceptance Test Flight Laser Delivery

Additi l Th lAdditional Thermal Characterization at

Fibertek

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Both laser's outputs were unchanged at the end of full space-qualification testing

FIBERTEK, INC. Laser Build & Qualification Issues

Space-qualified electronics were more expensive to build and test than anticipatedthan anticipated

– Use of radiation hard parts required complete redesigns of previously used electronics

– Laser Electronics Unit test plan required almost 2 man years of effort to developto develop

> Software Flight Qualification Test was more extensive than originally planned to meet NASA requirements

> Software test procedure alone was >70 pages and was executed 5 times

Conducted EMI due to pulsed power draw required addition of large EMI filter by Ball

Subtle power supply changes surfaced intermittent start up glitches after space craft integration and required modification toglitches after space craft integration and required modification to the Laser Control Board

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FIBERTEK, INC. Space-Qualifiable LaserDesign Guidelines

Use mature laser technologies– The cost and schedule constraints of a space-based lidar mission coupled with the

logistic complications of any "routine" space mission provide ample opportunities for failure without even introducing a significant technology risk component.

Use alignment insensitive resonator designsUse alignment insensitive resonator designs– Typical lidar boresight requirements tolerate >100 μrad raw beam wander– Many resonators exhibit significant power drop for 100 μrad misalignment

Develop and practice stringent contamination control procedures– The evolution of contaminants in an optical compartment is a one of the major long

term failure mechanisms in space-based lasers– Contamination control procedures developed in conjunction with Ball Aerospace

and NASA with were validated with lifetime testing

Operate all optical components at appropriately derated levels– Derating of optical components in lasers is less well defined than electrical and

mechanical components– The laser diodes used to pump the Nd:YAG gain medium were run at peak optical p p g p p

powers derated by >30% of their design values– The power density in the Nd:YAG slab is 1/3 the damage threshold. For all other

optics the fluence/damage threshold ratio is <1/4

Budget properly for the space-qualification of the electronics and software

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g p p y p q– The most programmatically difficult area for the CALIPSO laser transmitter was

meeting the planned cost and schedule for building and qualifying electronics

FIBERTEK, INC.

Orbital Laser Performance

CALIPSO launched on April 28, 2006

Health of the electronics and internal pressure verified for both lasers ~ 2 weeks later

Laser #2 was successfully operated at full power on May 23– Total power unchanged, small balancing of 1064 nm/532 nm needed– A lidar ground return was observed without on orbit alignment of the laser

transmitter assembly pointing.

The laser was shutdown to allow final orbit correction maneuvers and was restarted June 6 after the satellite had entered the A-Train

– Final laser and lidar alignments performed week of June 5

First lidar data released June 9

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Short Term On Orbit Stability

Dual wavelength energy monitor - high precision measurements of both 532 nm

and 1064 nm shot to shot energies- On orbit shot to shot energy stability is ~0 3%

June 10, 2006 energy monitor data

On orbit shot to shot energy stability is 0.3%- < 0.1% energy trends can be measured with

modest averaging

Sept. 7, 2007 energy monitor data

O ill ti i th it d tOscillations in the energy monitor data are due to orbital temperature variation. Peak

to peak value of oscillations are ~1 mJ.

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FIBERTEK, INC. Laser Energy Trends

Total laser energy is down 5.2% since lidar commissioning in early June 2006- From 6/06/06 to 9/9/07 the total energy dropped from 227.0 mJ to 215.2 mJ- 4.2% per year energy decrease is consistent with pre-launch life testing

O h lf f d i d t 6 b d tOver half of energy drop is due to 6 bar drop outs - Non-catastrophic dropouts expected

Total on orbit shot count is over 750 million

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FIBERTEK, INC. Energy Decrease Details

Total 532 10647/15/2006 1.44 0.80 0.64 28/24/2006 1.10 0.48 0.62 1

11/30/2006 0.96 0.55 0.41 13/10/2007 1 47 0 80 0 67 2

Deltas (mJ)Date

Diode Bank

1

3/10/2007 1.47 0.80 0.67 26/20/2007 0.94 0.42 0.42 28/7/2007 1.13 0.70 0.43 18/22/2007 1.92 1.01 0.91 1

112

3 45

6Solar Flare

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Compensation for Energy Decrease

Total energy decrease to date is equivalent to loss of 10 of 192 diode bars

Diode pump pulse width ground control commandable– Current value is 144 µs– Increase to to over 200 µs possible

Diode temperature is off optimum for better λ match to etalon in 532 nm p preceiver channel

– Cooler operation can increase output energies

L M d li R l

Total Energy (mJ) # of Bars

Pedestal Temp (°C)

Pulse Width (µS)

Laser Modeling Results

(mJ) # of Bars Temp (°C) (µS)215 182 17.3 144230 182 17.3 154220 182 15 45 144

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220 182 15.45 144

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Laser Canister Pressure Trends

Pressure loss will limit on orbit life of Laser SN #2- Pressure trend fit predicts ~3 years to 2X corona limit- Meets planned mission life of 3 years

Laser SN #1 pressure trend exceeds planned mission lifeLaser SN #1 pressure trend exceeds planned mission life- Pressure decrease is < 3% in 15 months

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Acknowledgements

We wish to acknowledge the support of Pat Lucker, Bill Hunt, and Dr. David Winker at the NASA Langley Research Center; and Lyle Ruppert and Justin Spelman at Ball Aerospace & Technologies Corp. for their support in the generation and analysis of the data in this presentation

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